   A group is just a string"
   [{storage :storage} feature-name group]
   (update-in-storage
+    feature-name
     (fn [feature]
       (update-in feature
                  :groups

  percentages are out of 100"
  [{storage :storage} feature-name percent]
  (update-in-storage
    (fn [feature]
      (assoc feature
             :percentage

  "completely activate a feature for all users"
  [{storage :storage} feature-name]
  (update-in-storage
    feature-name
    #(assoc %
            :percentage
            100)))
